1. Field of the Invention
The present invention relates to a recording medium storing a computer program for determining an exposure parameter, an exposure method, and a method of manufacturing a device.
2. Description of the Related Art
In the field of semiconductor manufacturing lithography, predetermined patterning is performed using a reticle. To expand the production volume, an exposure apparatus is often newly introduced.
The model of the newly introduced exposure apparatus may be the same as or different from the conventional exposure apparatus. When a new exposure apparatus is introduced, there arises a need for an operation for enabling the exposure apparatus to form the same pattern as the conventional pattern on a substrate using the conventional reticle. This operation is commonly called pattern matching.
Exposure parameters which have the greatest influence on the pattern shape on the substrate are the illumination condition of the reticle and the numerical aperture (NA) and aberration of the projection optical system. Naturally, first, such exposure parameters for the new exposure apparatus are set to the same values as those for the conventional exposure apparatus. However, if the new and old exposure apparatuses are of different types, a definition which represents the illumination condition differs between them. In this case, the same illumination condition is not obtained despite the use of the same numeric representation, making it impossible to form the same pattern. The same applies to the NA, but the difference in definition between the new and old exposure apparatuses in this respect is too small to be really problematic. The aberration also influences the pattern shape, but a leading-edge exposure apparatus has less aberration and its contribution is therefore negligible. Accordingly, although it is a common practice to achieve the object of pattern matching by adjusting the illumination condition, it is not easy to obtain high matching accuracy.
The conventional pattern matching method will be explained below. The illumination condition, the exposure amount, and the defocus amount (typically, a best focus position) are specified, and the contour of the reticle pattern on the substrate is calculated. The RMS (Root Mean Square) value or maximum value of the differences between target values and calculated values at a plurality of pattern matching positions is obtained and the obtained value is set as an index value. FIG. 3 illustrates one example of this method. The target values, the calculated values, and the plurality of pattern matching positions are indicated by dotted lines, solid lines, and alternate long and short dashed lines, respectively.
Next, the illumination condition is slightly changed while keeping the exposure amount and the defocus amount the same, and an index value is obtained. By repeating this sequence in the space to set the illumination condition, an illumination condition under which the index value is minimum is obtained.
The conventional pattern matching method can ensure high pattern matching accuracy as long as the exposure amount and the defocus amount do not fluctuate. However, because the exposure parameter is optimized at a limited exposure amount and defocus amount, the degrees of freedom of the exposure amount and defocus amount may be insufficient under the illumination condition obtained in this way.